Many applications today call for the fabrication of components from "composite" materials, also known as fiber-reinforced plastics. Fiber-reinforced plastics are comprised of reinforcing fibers that are positioned in a polymer matrix. Commonly, the reinforcing fibers are fiberglass, although high strength fibers such as aramid and carbon are used in advanced applications, such as aerospace applications. The polymer matrix is a thermoset resin, typically polyester, vinyl ester, or epoxy. Specialized resins, such as, phenolic, polyurethane and silicone are used for specific applications.
Composite materials may be formed using numerous fabrication process. One such process that is common in the aerospace industry is a lay up process. In a typically lay up process, layers of reinforcing fiber are laid in a mold by hand or by a placement machine. Liquid resin is then poured on the fiber materials such that the resin fills the spaces between the fibers. The materials may then be cured at room temperature or in an autoclave and the liquid resin turns into a solid thermoset. The fibers are thus impregnated in the solid thermoset resin and reinforce the resin. Alternatively, layers of fibers can be pre-impregnated with resin and then partially cured to form layers of "prepreg" material. After this partial curing, the resin has not completely set, and the prepreg layers are flexible and can be shaped in or around a mold or forming tool. Once the prepreg layers are so shaped, the prepreg is then completely cured in an autoclave to form a fiber-reinforced laminate.
Composite structures often have several discrete composite components. For example, composite aircraft structure includes a composite skin, a number of stiffening members and other support structures. In metal aircraft wings, the various parts are formed separately and then fastened together using fastening methods such as welding and riveting. However, due to the nature of composite components, such fastening methods are not useful. Instead, the composite components are typically formed together using methods such as lay ups and autoclave curing, described above.
Due to the nature of forming tools that are traditionally used, these components are typically fabricated in a sequential fashion. For example, in the fabrication of a composite wing, the skin is first molded and cured. One set of stiffening members is then formed on the wing skin, and the entire structure is cured again. Further stiffening members and other structural supports are then sequentially added to the structure and cured. This method of fabrication is extremely expensive and time-consuming, and greatly increases the costs of advanced composite structures such as aircraft components.
Therefore, a need has arisen for a new method and apparatus for fabricating composite structures that overcomes the disadvantages and deficiencies of the prior art.